The hope is that the much sought after female cichlid will be found in a private collection somewhere around the world

"They are unusual fish compared to many in that they practise pair bonding and parental care of the eggs and the fry, so there's a lot of tussling that goes on between them."

Having carried out a search with other aquariums around the world and failed to find a mate for their bachelor boys, the team at the Zoological Society of London are now hoping that someone may have a female in a private collection.

According to Mr Zimmerman, if you have one you're likely to know it.

"They are not a particularly beautiful fish - they are gorgeously ugly, they are unusual. They are more a connoisseur's type of fish. They need quite a bit of space; the males are bigger than your hand, and they need a decent tank," he added.

Given the age profile of the London males and the failure to find a mate in the world's zoos, Mr Zimmerman is not very confident for the future of the species.

"I'm not very hopeful. This freshwater fish crisis is huge worldwide, and as water becomes diverted for human use it becomes scarcer and fish generally lose out," he said.

"I think there's probably a very slim to no chance of this fish surviving."

London Zoo is asking anyone with information about female cichlids to email the team at fishappeal@zsl.org